For the cake
Cooking spray, for pan
1 box vanilla cake mix
1 (3.4-oz) package instant vanilla pudding
4 large eggs
1 c. water
1/2 c. (1 stick) butter, melted
For the frosting + topping
1/2 c. (1 stick) butter, softened
2 c. powdered sugar
1 tsp. pure vanilla extract
2 tbsp. heavy cream
Pinch of kosher salt
1 qt. strawberries, stems removed
2 c. Cool Whip
Preheat oven to 350°. Line two 8” round cake pans with parchment paper and grease with cooking spray. In a large bowl, beat together cake mix, pudding mix, eggs, water, and butter. Divide between prepared pans and bake until a toothpick inserted into the middle comes out clean, 25 minutes. Let cool completely.
Meanwhile, make buttercream: In a large bowl using a hand mixer or the bowl of a stand mixer using the paddle attachment, beat butter until fluffy. Add powdered sugar and beat until combined, then add vanilla, heavy cream, and salt and beat until combined.
Spread a thin layer of buttercream on top of one cake layer, then transfer remaining buttercream to a piping bag. (No need to use a pastry tip — just ship a large hole!) Stand strawberries on top of buttercream in an even layer then pipe buttercream between and top of strawberries to cover. Smooth top with an offset spatula.
Place second layer on top, then cover the entire cake with Cool Whip. Slice any leftover strawberries into thin slices to garnish cake.